Generic ozonisers comprise a plurality of ozone generators, arranged in parallel to one another between two tube sheets in the manner of a tube-bundle heat exchanger. Internally, the tubes create discharge chambers in the form of hollow cathodes. Anode rods with dielectric are arranged in these discharge chambers, which during operation are impinged upon by a high voltage and which cause a silent discharge between the anode rod and the tube. An oxygenated gas or pure oxygen is passed through this interstice. The silent discharge generates ozone molecules in the oxygenated gas from oxygen molecules. The gas flow enriched with ozone in this way can, by way of example, be used for disinfection purposes.
Most of the electrical power that has to be supplied to an ozone generator results in waste heat. This waste heat is dissipated by cooling measures, such as for example liquid cooling of the outer electrode. Here, the cooling water heats up as it passes through the tube bundle and is cooled to a temperature of a few degrees Celsius in a circuit by a heat exchanger in a cooling unit.
A mechanism that impairs the efficiency of an ozoniser is the unavoidable temperature gradient that arises along the tubes between the cooling water entry and the cooling water exit.
The efficiency of ozonisers is highly dependent on the temperature in the discharge gap. The formation of ozone preferably takes place at low temperature. In addition, the ozone increasingly disintegrates as the temperature rises. This temperature-induced ozone depletion reduces the overall efficiency of the ozoniser. To raise the ozone yield, therefore, a targeted manipulation of the effective reaction temperature along the ozone generator is desired.
An ozone generator is known from JP-H-0881205 having a conical outer electrode, in contact with a dielectric, which in a first embodiment has a thickness that increases along the length of the ozone generator and in a second exemplary embodiment has a constant thickness. What these arrangements have in common is that the power recorded in the gas gap decreases continuously over the length of the ozone generator. In this way, the increase in temperature over the length of the ozone generator is reduced, as a result of which the effective reaction temperature can be kept almost constant. The disadvantage here is that the manufacture of the outer electrode and of the dielectric is relatively complicated and cost-intensive.